In many computers, data is often input through use of a pointing device that moves a cursor on a computer screen. By pressing one or more buttons on the pointing device, the user can then select a menu item, highlight a portion of the display, select a screen region for inquiry or other action, select hypertext (in, e.g., a Web browser), or perform numerous other activities well-known to computer users. One such pointing device, and perhaps the most ubiquitous, is commonly referred to as a “mouse.” Typically, a mouse is molded to comfortably fit a user's hand; contains internal sensors for detecting, measuring and encoding movement of the mouse across a desktop, mouse pad or other surface; and is connected to a computer by a cord or a wireless connection. A mouse typically has two or more buttons that a user can press to make a selection. FIG. 1 shows a typical mouse.
Although most mice operate according to the same overall scheme (i.e., movement across a surface is translated into cursor movement), internal components and designs vary widely. For example, many mice detect and measure movement through use of a ball that rolls as the mouse is moved across a mouse pad or other surface, with the ball in turn moving encoder wheels. Other designs use a Light Emitting Diode or other source and an accompanying detector to measure movement by reflection from surface irregularities of a desktop or other surface. Some mice receive power and communicate with a computer through a cord, while “wireless” mice may be battery powered and communicate by infrared (IR) or radio frequency (RF) radiation. Although most mice have at least primary and secondary buttons for user input (the familiar “right-click” and “left-click” buttons), other mice have additional buttons (used for, e.g., forward and backward browser selection, etc.), scroll wheels, etc.
Despite the wide variety of mouse designs and options, most computer mice use switches having an internal mechanism that relies upon deforming a metallic component. These switches typically have an internal metal beam or disc that is encased in a plastic housing, and which is then soldered or otherwise attached to a printed circuit board within the mouse. When the user presses a mouse button, a plunger or post on the bottom of that button pushes down upon the metal disc or strip, acting against the spring-loaded bias of the metal to move the beam (or disc) into a position to close a circuit. FIG. 2 shows one such arrangement in an exploded view of a conventional mouse 100, with the lower case and other components omitted for the purpose of clarity. As the user depresses one of the buttons 101 movably attached to the mouse upper case 105, a post attached to the underside of button 101 moves downward. In an assembled state, the end of that post is over, and acts upon switch 150. Switch 150 is attached to printed circuit board 135, which is in turn attached to upper housing 100 and/or a lower mouse housing (not shown). FIG. 3 shows additional details of a prior art switch in operation in this example of a metallic disc switch. FIG. 3 is a partially schematic cross-section of switch 150. Located in the bottom of lower housing 158 are electrical contacts 151 with associated leads 157. Resting above contacts 151 is a metallic disc 152. As shown, the disc is normally bowed upward, and the contacts 151 are not closed. When post 102 moves downward, it pushes upon a plastic cap 154 (held by upper housing 155), which in turn presses down upon a rubber plunger 153, which in turn collapses disc 152 to close contacts 151. Upon release of the downward force of 102, the disc 151 returns to the upwardly bowed state.
FIG. 3A is a schematic drawing of a metallic beam switch. As post 102′ moves downward (because of the user depressing a mouse button), spring beam 182 is also pushed downward and into one of conductive contact 181 mounted on circuit board 135′. When the user releases the mouse button, the resiliency of spring beam 182 biases spring beam 182 away from contact 181.
These types of prior art switches have disadvantages. For example, these switches are relatively expensive, and thus increase the cost of manufacturing a computer mouse. For this and other reasons, there remains a need for a computer mouse with a less expensive and otherwise more advantageous type of switch mechanism.
Elastomeric dome switches are another type of switch that has been used in mobile telephones, remote controls units, keyboards and other electronic devices. Typically, these switches are made from an elastomeric compound such as silicone, and have a concave, dome-like structure. The underside of the dome typically has a contact member located therein. When sufficient downward force is exerted on the dome, the upward bias of the elastomeric dome is overcome, causing the dome to collapse. The contact member on the underside of the dome is thereby brought into contact with exposed conductive leads, a membrane switch, or other open electrical elements; and the electrical connection is thereby closed. When the downward force on the dome is released, the upward bias of the dome moves the contact member out of contact with the other switch elements, thereby opening the electrical connection.
While dome switches are inexpensive and reliable, it has generally been believed that their characteristics make them unsuitable for use in devices such as computer mice. Specifically, because of their inherent properties, prior art dome switches have been used in devices with relatively slow response speeds and large travel distances. By contrast, mouse buttons are often pressed in more rapid succession (e.g., the familiar “double-click”), and the return rate of existing elastomeric switches is not well suited for use in such a context. Similarly, the travel distance and applied force to activate a computer mouse button make existing elastomeric dome switches ill-suited in this regard.